Constitutional Diagram of Ternary Fe-Ca-Si Alloys

Microstructural observations, thermal analyses, chemical analyses and X-ray diffractions have been made of the alloys melted with arc or high-frequency induction in argon atmosphere, the compositions of which lie in the field of two-liquid immiscibility and one-liquid phase. The results may be summarized as follows : With increasing content of silicon or of aluminium, the miscible gap of the field of the Fe (Mn)-Ca system became narrow and had a critical point at nearly 33% Fe (Mn)-33%Ca-34%Si(Al), at which the two-liquid phase became indistinguishable. Above 35% silicon or aluminium content, only one liquid solution existed over the entire composition range of the alloy system. It was assumed that a quasi-binary eutectic point should appear in the vicinity of 23%Fe-38.5%Ca-38.5%Si for a quasi-binary system existing between the binary intermediate compounds CaSi and FeSi. Freezing of alloys involving ternary three-phase equilibrium was completed at 1030℃ and the composition of this ternary non-variant point lay upon 5%Fe-35%Ca-60%Si. In the field of only one liquid solution there were four primary phase regions of Si, CaSi, FeSi and FeSi_2. As morphological features, Si appeared in rectangular form, FeSi in dendritic or spherical form, and CaSi and FeSi_2 in band or plate-like form

Effect of the Additions of Barium-bearing Calcium Alloys on the Dissolved Oxygen and Sulphur of Liquid Iron

In order to investigate the effect of barium-bearing calcium alloys on the oxygen and sulphur content of liquid iron, deoxidation of liquid iron with CaBa, CaSi, and CaSiBa deoxidizers was studied at 1600℃ using a high frequency induction furnace, a lime crucible and mechanically mixed basic powder. The results indicate that barium in the calcium alloy enhances the deoxidation of liquid iron in the early time and then CaO type inclusions with very small concentrations of barium are possible to identify by a microprobe analyser. By Al plus CaSiBa addition decreases final total oxygen levels in the range of 10 ppm to 20 ppm. The sulphur content of the melt is reduced from 50 ppm to below 3 ppm

Process of Graphite Precipitation in Calcium Graphite Steel

The effect of calcium on the graphite precipitation from the γ phase of a hypereutectoid steel has been examined with an apparatus newly designed for the measurement of solidifying contraction. It was ascertained that the graphite precipitation in the solidifying process occurred over the range from the vicinity of the saturation curve E\u27S\u27 of the γ phase (Agr point) to the A_1 point, and that the graphitization took place most remarkably near the A_1 point. The addition of a large amount of metallic calcium or of Fe-Ca-Si alloy greatly affected the solidifying contraction curve, leading to a considerable expansion due to ferrite formation near the A_1 point. In this case the rise of the A_1 point was not observed, although Si content increased. The addition of Fe-Ca-Si alloy as the graphitizing agent increased the amount of residual calcium more than that in the case of the addition of metallic calcium

Effects of Sulphur, Oxygen and Silicon on Graphite Precipitation in Calcium Graphite Steel

Effects of sulphur, oxygen and silicon on the graphite precipitation in calcium graphite steel were investigated. Sulphur greatly hindered the precipitation from γ solid solution. According as the amount from 0.03 to 0.18% of sulphur, primary cementite appeared not only in the matrix but also in the grain boundary. With increasing oxygen content above 0.008%, graphitization decreased and also primary cementite crystallized out preferentially from the γ solid solution. When the hypereutectoid steel was melted in vacuum, graphitization did not occur without a suitable addition of silicon. Fundamental conditions on graphite precipitation by the calcium treatment were summarized in the following three points : (1) effect of deoxidization and desulphurization, (2) instabilization of cementite to precipitate from the γ solid solution, and (3) formatian of crystal imperfections such as voids in the solidifying process. Effective acceleration of graphite precipitation due to silicon was also discussed

On the Embrittlement and Toughness of High Purity Fe-30Cr-2Mo Alloy

Experiments were conducted to explain unexpected embrittlement phenomena encountered in fabricating a high purity Fe-30Cr-2Mo alloy. By means of a hydrostatic tensile test with a Bridgman-Type specimen it was found that the fracture behaviour of the alloy is highly dependent on stress state. Under conditions of low triaxial stress, the alloy displays excellent ductility. Under conditions of high triaxial stress, however, the alloy shows less strain to fracture and a transition from ductile to cleavage fracture. The toughness of the Fe-30Cr-2Mo alloy can be significantly improved by thermomechanical processing

The Effect of Melting Condition on the Properties of High Chromium Ferritic Steels(Metallurgy)

The influence of melting atmosphere and impurity elements on the hot workability of Fe-30%Cr alloys and the effect of vacuum and Ca refining on the mechanical properties have been studied. The results obtained are as follows. The deformation resistance of zone refined heat with the lowest impurity content is from 23 to 13 kg/mm^2 in the temperature range of 850°to 1300℃. Increasing the interstitial elements such as C and N in the vacuum-melted heat raises the deformation resistance in any hot-working temperature. However, the contents of O up to 0.2%, S up to 0.1%, Mn up to 2%, Si and Al up to 0.5% have not any significant effect on the deformation resistance. The heats of more than 0.017%C reveal intercrystalline fracture from above 1200℃. The crack initiations due to the cluster of alumina or chromium oxide inclusion are also observed. It is ascertained that the globular type inclusions found in the vacuum and Ca refined heats consist mainly of calcium aluminate, and their tensile strengths are approximately 45 to 65 kg/mm^2 with elongations of 28 to 35% at room temperature -72°and -120℃, and the ductile fracture with a fine dimple pattern is observed

Grain Structure and Precipitation of Aluminium Nitride in Aluminium and Calcium Deoxidized Low Carbon Steels

The effects of cold reduction, annealing temperature, heating rate and thermal history before cold reduction on the recrystallization in silicon-deoxidized, aluminium-deoxidized and aluminium-calcium-deoxidized low carbon steels were investigated by means of microscopical observation, hardness test, chemical analysis and low frequency internal friction measurement. The recrystallization behaviour of aluminium-deoxidized and aluminium-calcium-deoxidized steels differed from that of silicon-deoxidized steel, and in the former two steels annealed the structure of elongated grain was obtained as compared with that of equi-axed one in the silicon-deoxidized steel. By means of low frequency internal friction measurement, it was shown that in the steel of elongated grain structure the lowering of dissolved nitrogen occurred during the period from the recovery to an early stage of recrystallization. This would suggest that the nitrogen, at this stage, existed either as preprecipitation clusters with aluminium or as very fine precipitates of AlN. The mechanism of the formation of elongated grain was considered in terms of the effectiveness of AlN precipitation during recrystallization

Deoxidation and Desulfurization of Liquid Steel with Calcium Complex Alloys

In order to know the effect of calcium alloy on the change in the contents of oxygen and sulfur in liquid steel, the deoxidation of steel at 1600℃ was studied by the use of different calcium complex deoxidizers under the condition of the high frequency induction melting in a magnesia-lined crucible, with a covering of unslaked lime to a depth of 10mm. The results obtained are summarized as follows : (1) Although the oxygen content decreased up to 0.004% in the case of the addition of 2%SiMn, either by the addition of one lump sum at a time or by the divided additions of the same sum, the desulfurization did not significantly proceed. By the addition of calcium complex deoxidizers containing aluminum, after lowering the oxygen content, the sulfur content decreased considerably below that obtained by the addition of CaSi, CaSiMn, or CaSiBa. (2) When the oxygen content was constant, the greatest desulfurization was obtained by the divided additions of calcium complex deoxidizers containing aluminum ; that is, the S/O ratio became as low as the value of about 0.67 to 0.90, in comparison with the value of 2.3 which was obtained with CaSi or CaSiMn. (3) According to the results of electron-probe microanalysis, the compositions of the non-metallic inclusions in ingots, which were produced by the addition of calcium complex deoxidizer containing aluminum, were in such wide concentration ranges of CaO (26 to 46%), Al_2O_3 (40 to 54%), and CaS (to 34%) as indicated the presence of complex oxy-sulfide inclusions. (4) It is suggested from the differences in the yield of silicon and aluminum in ingots and in the ratio of desulfurization to deoxidation that the calcium complex alloy having the ratio of Al : Ca : Si : Mn : Fe=1 : 1 : 1 : 1 : 1 is favorable for the deoxidizer

Precipitation of Aluminium Nitride during Recrystallization of α-Iron

An investigation has been made on the precipitation of A1N in vacuum melted iron wires containing 0.003, 0.036, and 0.072 wt% Al, solution-treated at 1200℃, cold-reduced to 70%, and isothermally annealed in the range 500°to 700℃. The behaviour of A1N in α-iron during annealing was followed by low frequency internal friction measurement. By separating the observed Snoek peaks into those of carbon and nitrogen, the amounts of carbon and nitrogen dissolved in solution were determined. The results obtained were summarized as follows : (1) In Fe-0.003 wt% Al, nitrided or carburized prior to the solution-treatment, the amount of dissolved nitrogen was increased during isothermal annealing at 600℃ after cold reduction, whereas the amount of dissolved carbon decreased to the solubility limit. (2) Some difference was seen in the process of A1N precipitation during isothermal annealing between Fe-0.036 wt% Al-0.006 wt% N, in which the A1N particles were completely dissolved by a solution-treatment at 1200℃, and Fe-0.072 wt% Al-0.028 wt% N, in which some of the A1N particles remained undissolved. A1N precipitation in both cases occurred during the recovery and in the early stage of recrystallization at 600℃, and the recrystallization was retarded. (3) In Fe-0.072 wt% Al-0.028 wt% N annealed at 700℃, the recrystallization was completed before A1N precipitation started. However, a preheat-treatment of for 20 hr at 500℃ given prior to 700℃ annealing did significantly affect the recrystallization process by promoting A1N precipitation and decreasing the recrystallization rate

Graphite Re-precipitation in Calcium Graphite Steel

Metastable primary cementite precipitates preferentially from the γ solid solution of hypereutectoid Fe-C steels, without stable graphite precipitation, by the ordinary solidifying process. In the present experiment, it was found that graphite re-precipitation readily occurred from the γ solid solution of calcium-treated hypereutectoid cast steels during the air-cooling or the furnace-cooling after the heat-treatment in the y region from 1060℃ to 1210℃. In calcium-untreated cast steels, graphite precipitation was observable mainly along the grain boundaries of dendritic structures by the furnace-cooling from 1000℃ immediately after rapid cooling from the molten state to that temperature. If crystal imperfections such as voids are formed in the γ solid solution, the graphite precipitation would more readily occur in those sites, because the activation energy for graphite nucleation decreases due to decreasing interfacial energy and strain energy. On the basis of the experimental results hitherto obtained, the mechanism of graphite precipitation from the γ solid solution was considered